Links

Blender

Export Options (so that the object is not lying on the side after Export/Import):

Forward: Y Forward

Up: Z up

Changing the object's origin to its bottom:

Switch to Edit Mode if needed (Tab). With vertex selection on, choose the center vertex in the bottom. Press Shift+S and choose Cursor to Selected. The 3D cursor will move to the selected vertex. Deselect all and switch to Object Mode (Tab).

In Tools choose Set Origin and then Origin to 3D Cursor.

Make sure the object's coordinates are set to 0,0,0. Now the object should be placed properly on the XY plane.

C++

Variable names

If you want to use real variable names but have nice names in the UE editor too, then use meta/DisplayName

owner / client /server

The instance that spawned the class is always ROLE_Authority. If an Actor is spawned on the client, the client is the authority.
-- OmaManfred

OmaManfred::

And concerning the owner stuff:
When you spawn an instance of a class on the server FOR Client A, you have to set him as the owner.
FActorSpawnParameters params;
params.Owner = PlayerAPlayerController;
SpawnActor<Class>(Class:StaticClass(),params);
Then on Client B you can say IsOwner(PlayerBPlayerController), which should return false.

Logging

The following is just a copy/paste/change from the UE4 wiki and was really done from different persons, I am just using the work of different people here.
Put it in a Log.h and include it into your <your_project>.h file after the #include "Engine.h".
Because <your_project>.h is in every of your files, you will now be able to use these macros in every .cpp file.

Am I client or server ?

To answer questions 1 and 2: you can use AActor::GetNetMode()
which returns whether you are a listen server, dedicated server or network client.
if (GetNetMode() == ENetMode::NM_ListenServer)
{
}
The ENetMode values are:
NM_Standalone = 0
NM_DedicatedServer = 1
NM_ListenServer = 2
NM_Client = 3 // is only when you are actually connected to a server
The ordering of the ENetMode values allows you to check multiple things at once:
GetNetMode() <= 2 means you are the server or standalone, so you have 'global authority'.